How do I determined the capacitance that is needed in a circuit?

How do I determine what capacitors do I need in a circuit. For example, to make a LED blink. Thank you for your help.

iceng5 years ago
Put some easy values and see if the blink duration is ok
then is the off time acceptable. If not long enough increase R and C..
If the off time is short, increase the value of R1.and C1....

Repeat until satisfied..

The most common way to get flashing LEDs is to use a 555 timer. The formulas to calculate the resistors and capacitor needed are on the wikipedia page, and will also be on the datasheets for the 555. There are a number of guides on this site to using the 555 and picking the right component values.